Process of drawing filaments



June 19, 1962 H. F. HUME ETAL 3,039,171

PROCESS OF DRAWING FILAMENTS Filed June 9, 1960 F I 6 I F I G. 2

W W W STEAMED I WED l GATHERED DRAWN DRAWN GATHE RED STEAMED DRAWN bRAwuGATHIERED United States Patent 3,039,171 PROCESS OF DRAWING FILAMENTSHarold F. Hume and Norman Radow, Wilmington, Del., assignors to E. I. duPont de Nemours and Company, Wilmington, DeL, a corporation of DelawareFiled June 9, 1960, Ser. No. 34,897 7 Claims. (Cl. 28--72) Thisinvention relates to novel and useful poly-amide filamentary structures,and more particularly, to such structures having increased shrinkagepotential.

It is well known to those skilled in the production of syntheticfilamentary structures that filaments having a high shrinkage potentialprovide many improvements. High shrinkage filaments may be combined withfilaments having a lower shrinkage to produce a bulky filamentarystructure after suitalble treatment, e.g., after immersing it in boilingwater for a suitable period. Such bulky structures are useful inproducing fabrics having an improved surface appearance and particularlyin the production of fabrics having the surface appearance of the moreexpensive spun yarn fabrics.

It has been found particularly difficult to produce highly crystallinepolyamide filamentary structures with a high shrinkage potential. Whilesome slight difference in shrinkage values may be achieved by the use ofdifferent draw ratios, this procedure causes undesirable differences inthe dyeability of the two components in the fabric. In addition, theshrinkage diiferences obtainable in this manner are not adequate formany end uses.

It is accordingly an object of this invention to provide a process forproducing yarns containing polyamide filaments having increasedshrinkage potential. Another object is to provide a process forproducing a polyamide yarn comprising filaments of high and lowshrinkage potential, the high shrinkage filaments having substantiallythe same dyeing characteristics as the low shrinkage filaments.

The above objects are accomplished by a process comprising exposing afirst filamentary structure comprising a synthetic linear polyamidecomposition to an atmosphere having a relative humidity of at leastabout 90% and a temperature of at least about 65 C., drawing thestructure at a draw ratio between about 1.25 and about 3.5, to providethe structure with a shrinkage potential of at least about 1%, andcombining the drawn filamentary structure with a second filamentarystructure which has a shrinkage potential at least about 1% less thanthe shrinkage potential of the first structure.

Additional objectives will become apparent in the following descriptionof the various process variations which have been exemplified andillustrated in FIGURES 1-4.

In a preferred embodiment, the first filamentary structure is combined,after the high humidity heat treatment, with -a second filamentarystructure, which has not been drawn or subjected to the high humidityheat treatment, and the combined structure drawn at a draw ratio betweenabout 1.25 and about 3.5. This process embodiment has been illustratedschematically in FIG. 1 and described in detail in connection withExample II.

In another embodiment shown schematically in FIG. 2 and described inExamples I and IV, the treated filamentary structure is combined, afterdrawing at a draw ratio between about 1.25 and about 3.5, with a drawnpolyamide filamentary structure, which has not been subjected to thehigh humidity heat treatment. Preferably, the draw ratios imposed on thefilaments are about the same.

In the process embodiment illustrated in FIG. 3 and described in ExampleV, a filamentary structure composed of undrawn polyamide filaments isexposed to an atmosphere having a relative humidity of at least about90% 3,039,171 Patented June 19,1962

and a temperature of at least about 65 C. and drawn at a draw ratiobetween about 1.25 and about 3.5. The filaments are then separated intotwo groups. One of these groups is heated and permitted to relax inlength, preferably at least about 4%, at a temperature between about C.and about 200 C. and thereafter recombined with the other group offilaments.

In a highly preferred embodiment, a bundle of filamentary structures issplit into at least two groups, one of Which is treated under the highhumidity conditions and draw ratios as above, and then recombined withthe other group or groups. This embodiment has been illustratedschematically in FIG. 4 and described in detail in Example III.

By shrinkage potential" as used herein is meant that shrinkage in lengthwhich occurs when a polyamide filamentary structure is immersed inboiling water for 15 minutes and permitted to dry under little or notension.

The filamentary structures treated in accordance with this inventioninclude continuous monofilaments, continuous multifilaments, spun yarn,tow, sliver, top, roving or any other desirable shape. The filamentarystructures may be crimped or bulked if desired.

EXAMPLE I Polyhexamethylene adipamide having a relative viscosity of 41(as described in US. Patent 2,385,890) is prepared and extruded in theconventional manner using apparatus of the type disclosed in US. Patent2,217,743.

The grid and melt-pool temperature of this apparatus is maintained at290 C. and the molten polymer is blanketed with an atmosphere ofnitrogen. The polymer is extruded through the spinneret, which 'has 17holes of 0.009 inch diameter, to produce yarn having a final denier of90. The filaments are quenched by passing air transversely across thefilament bundle as shown in US. Patent 2,273,105.

The filaments are then passed at a rate of 10 feet per second through asteam treatment enclosure as described in U.S. Patent 2,289,860. Steamat 7.5 p.s.i.g. (pounds per square inch, gauge) is supplied to theenclosure and the yarn is exposed to the steam for a distance of 48inches. The filament bundle is then treated with a conventional finish,cold drawn and wound into a package at a speed of 300 y.p.m. in theconventional manner. The draw ratio is varied as shown in the tablebelow. A 225 yard skein or" each yarn is placed in boiling water for 15minutes and the amount of shrinkage determined after drying. Results ofthese tests are shown in Table I below. For comparison, shrinkage testswere also made on yarns spun in an identical fashion except that thesteam treatment was omitted. The tenacities of the various yarn sampleswere determined in the conventional manner and are shown below.

Table I Boil-off shrinkage, Tenacity, g.p.d. percent Draw ratio SteamedUnsteamed Steamed Unsteamed The steam treated filaments, drawn at a drawratio of I 2.5, are combined with unsteamed yarn of the same denier anddraw ratio and the combined yarn woven into a tricot fabric in theconventional manner. The tricot fabn'c, after the customary finishingtreatments, is observed to have a softer handle and better coveringpower than tricot fabrics made from yarn having no difference inshrinkage potential of the filaments, The difference in shrinkage valuesbetween the high and low shrinkage filaments in the yarn is about 5-6%.

EXAMPLE II Polyhexamethy-lene adipamide is prepared and extruded asdescribed in Example I except that the polymer is extruded through twoadjacent spinnerets, one spinneret having 7 holes of 0.009 inch diameterand the other spinneret having 6 holes of the same diameter. Thefilaments from the spinnerets having 7 holes are steam treated as inExample I while the filaments from the other spinneret by-pass the steamenclosure. The filament bundles are then combined, treated with aconventional finish, cold drawn to a ratio of 2.0x and wound on apackage in the conventional manner. The denier of the yarn is 40. Whenplaced in boiling water, the yarn becomes bulky due to the highershrinkage of part of the filaments. The difference in shrinkage valuesbetween the high shrinkage filaments and the low shrinkage filaments is810% when measured under tension free conditions.

EXAMPLE III Example II is repeated except that the filament bundles aredrawn separately to substantially the same ratio and then combined. Thedifference in shrinkage and other characteristics of the yarn aresubstatially the same as in Example II,

EXAMPLE IV Example I is repeated except that the spinning speed. is

900 yards per minute instead of 300 yards per minute.

Table II Boll-off shrinkage, percent Draw ratio Steamed Unsteamed NOROQs s s OCIOO EXAMPLE V Polyhexamethylene adipamide yarn of 70 denier and24 filaments is prepared, extruded, quenched, steamed and finished asdescribed in Example I. The filaments are then divided into two bundleseach of denier and 12 filaments and the two resulting yarns wound intoseparate shapes.

Bobbins of the 3S denier 12 filament y-arn are placed in adjacentpositions on a draw twisting machine. One of the yarns is drawn 2.5 inthe conventional manner, then passed through a steam chamber where it isheated to a temperature of about 120 C, by the action of the steam,after which it is passed around the end of the draw roll, which is ofsmaller diameter than the rest of the roller, to permit the yarn toshrink about 10%. The yarn is then passed to the adjacent position onthe machine where it is combined with the other yarn which haspreviously been drawn 2.5x without the steam treatment. The yarn is thentwisted 1 to 2 turns per inch as it is wound into a pirn.

When the yarn is subjected to boiling water as in Example I the yarnbecomes bulky due to the difference in 4 shrinkage of the filaments. Thedifference in shrinkage values between the high shrinkage and lowshrinkage filaments is 8%.

Optimum product characteristics are provided only when filamentarystructures are treated under conditions of high humidity and temperatureand drawn at ratios within a critical range. The filamentary structuresare conveniently heated with steam to provide the proper conditions oftemperature and humidity, although other methods may also be employed.The filamentary structures may, for example, be wet with water oraqueous finish solution and then heated by any suitable means to therequired temperature.

In order to provide the necessary increment of shrinkage over normalyarns, the filamentary structures must be drawn within the critical drawratio range as well as subjected to the high heat and humidityconditions. While appreciable differences in shrinkage may be obtainedover the draw ratio range of 1.25 to 3.5, draw ratios within the rangeof 2.0 to 2.5 are preferred for the best combination of yarn strengthand shrinkage. The peak shrinkage value at these draw ratios is indeedsurprising and is contrary to what would be expected, i.e., higher drawratios have been considered in the past to provide higher shrinkagepotential values.

Improved yarn properties, particularly cover and hand, are obtained whenthe high and low shrinkage filamentary structures differ by as little as1% in shrinkage potential, but preferred results are obtained when thesevalues differ from at least 5 to about 15%. Shrinkage potential valuesup to about 20% have been obtained and even higher values are deemedfeasible. In this regard, it is necessary to balance the shrinkagepotential and tenacity values desired for the particular fabric to beproduced.

In addition to their usefulness in combination with lower shrinkagepolyamide filaments, the highly shrinkable filaments of this inventionmay obviously be combined with low shrinkage filaments composed of otherpolymers to obtain yarns having desirable properties.

Among the suitable organic polymeric compositions there are includedpolyesters, such as poly(ethylene terephthalate); polyacrylonitrile andcopolymers containing at least by weight combined acrylonitrile, such asacrylonitnile (92%) methyl acrylate (7.5%) and sodium styrene sulfonate(0.5%); Polyhydrocanbons, such as polyethylene and polypropylene andmany others.

The preferred polyamides for use in the process of this invention arepoly(hexamethylene adipamide) and polyepsilon caproamide. Other suitablepolyamides include those described in US. Patents 2,071,252, 2,130,-523, and 2,130,948.

We claim:

1. The process comprising exposing a first filamentary structurecomprising a synthetic, linear polyamide composition to an atmospherehaving a relative humidity of at least about and a temperature of atleast about 65 C., drawing said structure at a draw ratio between about1.25 and about 3.5 to provide the structure with a shrinkage potentialof at least about 1%, and gathering saidfirst filamentary structure anda second filamentary structure into a bundle, said second structurehaving a shrinkage potential at least about 1% less than the shrinkagepotential of said first filamentary structure.

2. The process of claim 1 wherein the first filamentary structure iscomposed of poly(hexamethylene adipamide) filaments.

3. The process of claim 2 wherein the atmosphere comprises steam.

4. The process of claim 3 where-in said first and second filamentarystructures are both composed of poly(hexa methylene adipamide)filaments.

5. The process comprising exposing a first filamentary structurecomprising a synthetic linear polyamide composition to an atmospherehaving a relative humidity of at least about 90% and a temperature of atleast about 65 C., gathering said first filamentary structure and anundrawn second filamentary structure into a bundle and drawing thebundle at a draw ratio between about 1.25 and about 3.5, the shrinkagepotential of the second filamentary structure being at least 1% lessthan the shrinkage potential of the first filamentary structure.

6. The process comprising exposing a filamentary structure composed of aplurality of undrawn filaments comprising a synthetic, linear polyamidecomposition to an atmosphere having a relative humidity of at leastabout 90% and a temperature of at least about 65 (3., drawing saidfilamentary structure at a draw ratio between about 1.25 and about 3.5,separating the filaments of the drawn filamentary structure into a firstand a second group of filaments, heating said first group at atemperature between about 120 and about 200 C. while permitting thefilaments therein to relax in length, and gathering said first andsecond groups into a bundle.

7. The process comprising providing a bundle of filamentary structurescomprising a synthetic, linear polyamide composition, dividing saidbundle into at least two groups of filamentary structures, exposing oneof said groups to an atmosphere having a'relative humidity of at leastabout 90% and a temperature of at least about 65 C., subsequentlydrawing said one group at a draw ratio between about 1.25 and about 3.5to provide the structures therein with a shrinkage potential of at leastabout 1% and gathering said groups of structures into another bundle,the structures of said second group having a shrinkage potential atleast 1% less than the shrinkage potential of the filamentary structuresof the first group.

References Cited in the file of this patent UNITED STATES PATENTS2,174,878 Hardy Oct. 3, 1939

1. THE PROCESS COMPRISING EXPOSING A FIRST FILAMENTARY STRUCTURECOMPRISING A SYNTHETIC, LINEAR POLYAMIDE COMPOSITION TO AN ATMOSPHEREHAVING A RELATIVE HUMIDITY OF AT LEAST ABOUT 90% AND A TEMPERATURE OF ATLEAST ABOUT 65*C., DRAWING SAID STRUCTURE AT A DRAW RATIO BETWEEN ABOUT125 AND ABOUT 3.5 TO PROVIDE THE STRUCTURE WITH A SHRINKAGE POTENTIAL OFAT LEAST ABOUT 1%, AND GATHERING